Solar cell modules, which are devices for converting the energy from sunlight into electrical energy, are attracting much attention as clean energy sources that are capable of generating electricity without discharging carbon dioxide, thereby responding to environmental problems such as atmospheric pollution and global warming.
Generally, a solar cell module includes basically solar cell that perform the photoelectric conversion, a encapsulant (filler layer) formed from an electrical insulator that encapsulates the solar cell, a front surface protective sheet (front sheet) that is laminated to the front surface of the encapsulant, and a back surface protective sheet (back sheet) that is laminated to the back surface of the encapsulant. The solar cell module requires sufficient moisture resistance and weather resistance to withstand use for long periods in outdoor and indoor environments.
The main structure of a solar cell module is composed of the solar cell that function as the photovoltaic elements, the encapsulant which is an electrical insulator that prevents shorts within the electrical circuits, and the protective sheets that protect the solar cell and the encapsulant. The front surface protective sheet and the back surface protective sheet are bonded to the light incident surface (front surface) and the back surface respectively of the solar cell module, and prevent water vapor from entering the solar cell module. These protective sheets for the solar cell module require excellent water vapor barrier properties, and must also exhibit excellent adhesion to the encapsulant of the solar cell module. One example of the encapsulant used in the solar cell module is an ethylene-vinyl acetate copolymer (hereafter also referred to as EVA).
A back surface protective sheet for a solar cell module has been disclosed in which a vapor deposited film of an inorganic oxide is provided on one surface of a substrate film, and an extruded resin layer formed from a resin composition containing a polyolefin-based resin and a cyclic polyolefin-based resin is then provided on the surface of the vapor deposited film of the inorganic oxide (for example, see Patent Document 1). This back surface protective sheet is fused to a encapsulant composed of an ethylene-vinyl acetate copolymer (EVA) by hot pressing.